Stirrer



Sept. 14, 1965 R. BURGER ETAL STIRRER Filed Nov. 20. 1963 Fig. I

INVENTORS' Robert Burger Pa trick M. Handke THE/R ATTORNEYS 1 United States Patent 3,206,173 STIRRER Robert Burger and Patrick M. Handke, Pittsburgh, Pa., assignors to Fisher Scientific Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 20, 1963, Ser. No. 325,069 10 Claims. (Cl. 259-414) This application relates to a stirrer, more particularly, a magnetic stirrer which avoids the insertion of any drive shaft journal or bearing into the liquid being stirred. The stirrer also avoids the creation of vortexes in the liquid while it is being stirred. It thereby provides for more uniform stirring of a liquid than has heretofore been possible, and this property makes it particularly useful in chemical determinations in which the addition of a single drop of reagent can produce a critical change in the liquid being stirred. In such determinations, there must be thorough stirring of the liquid after each drop of reagent is added and before a succeeding drop is added.

According to the present invention, the stirrer consists of a magnetic field generator which is positioned beneath a container for the liquid to be stirred and which moves a magnetic field in a circular path beneath the container so as to successively subject different portions of the space within the container to the effect of the magnetic field. The stirrer also includes a plate of magnetic material which is positioned within the container and which is subjected to the effect of the moving magnetic field. The plate is bent, at least once, about a line extending completely across the plate, and the portions of the plate extending from the bend line form a dihedral angle. As the magnetic field moves in a circular path beneath the container, it attracts towards it alternate portions of the plate on opposite sides of the bend line and thereby causes the plate to rock about the bend line. This rocking motion of the plate stirs liquid within the container.

In the accompanying drawings, we have illustrated certain presently preferred embodiments of our invention in which:

FIGURE 1 is a front elevation of our stirrer with a container for liquid to be stirred mounted in operative position on the stirrer;

FIGURE 2 is a plan view of the plate which is positioned within the container of liquid to be stirred;

FIGURE 3 is a side view of the plate looking in the direction of the arrows III-III in FIGURE 2;

FIGURE 4 is a side view of the looking in the diection of the arrows IVIV in FIGURE 2;

FIGURE 5 is a plan view of a modified form of stirring plate;

FIGURE 6 is a side View of the plate shown in FIG- URE 5; and

FIGURE 7 is an isometric view of the generator used to create a rotating magnetic field beneath the liquid container.

Referring to the drawings, FIGURE 1 shows the complete stirrer with a container for liquid mounted in operative position on the stirrer. The container is made of glass or other non-magnetic material. The stirrer comprises a housing 6 for an electric motor 7 which housing is closed by a cover 8 of non-magnetic material which forms a base for a container 9. The container 9 holds the liquid to be stirred and a stirring plate 10 rests on the bottom of the container.

FIGURES 2-4 inclusive show the plate 10 which is within the container 9 when the stirrer is in operation. The plate is circular in plan view and is bent along a bend line indicated by the chain line 11 in FIGURE 2. This bend line extends across the plate and portions of the plate extending from each side of the bend line form 3,296,173 Patented Sept. '14, 1965 a dihedral angle between them of more than as shown in FIGURE 3.

The plate has sufiicient area to cover a substantial portion of the bottom of the container in which it will be used. Preferably, it is circular in shape so that it will fit more conveniently in containers whose internal diameter approximates the diameter of the plate. Preferably, also, the bend line 11 passes through the center of the plate so that substantially equal portions of the plate extend from the bend line.

The plate 10 is also bent along a second bend line indicated by the chain line 12 in FIGURE 2. This second bend line extends across the plate and also at an angle (preferably a right angle) to the first bend line 11. As shown in FIGURE 4, the plate is bent about the bend line 12 in a direction opposite to that in which it was bent about the bend line 11, and the plate forms a hyperbolic paraboloid.

The plate is bent about two bend lines and in opposite directions at angles of more than 90 so that the plate can rest on either of its sides on the bottom of the container 9.

The plate 10 has a central, circular aperature 13 which contributes to the stirring action and facilitates the making of the two bends in opposite directions in the plate.

FIGURES 5 and 6 show a modified form of stirring plate. In this embodiment, a plate 14 is bent along only one bend line indicated by the chain line 15 in FIGURE 5. Several holes 16 are distributed across the surface of the plate to prevent it from rising in the liquid being stirred when the plate is being rocked about the bend line at relatively rapid rates.

The plates 10 and 14 may be coated with a chemically inert plastic material such as polytetrafluoroethylene so that its presence in the liquid being stirred will not contaminate the liquid.

The mechanism for creating a magnetic field which moves in a circular path beneath the container 9 is shown in FIGURE 1 and comprises the electric motor 7 which has a vertically extending shaft 17 which in turn supports a bar-shaped assembly 18 comprising a channel bar magnet and a counterweight. The assembly 18 is positioned beneath and extends generally parallel to the cover 8 which forms the base for the container 9.

Referring to FIGURE 5, the channel bar magnet and counterweight assembly 18 comprise a counterweight 19 having a horizontal extension or shelf 29 which supports a channel bar magnet 21 suitably secured to the extension. At the center of its mass, the assembly has a hub 22 which has a cylindrical opening 23 to mount the assembly on the shaft 17. The channel bar magnet has north and south poles as indicated by the letters N and S in FIGURE 5. The counterweight 19 and extension 20 are preferably made of an easily machined material such as brass or aluminum. The magnet 21, of course, is made of magnetic material. The weight of the counterweight 19 is such that it balances the channel bar magnet 21 and the extension 20 when the assembly rotates with the shaft 17 when the motor 7 is energized.

In operation of our stirring device, a container of liquid to be stirred is placed on the base 8 and a stirring plate 10 is dropped into the liquid. Whenever the magnet 21 passes beneath the plate 10 and to one side of a bend line in the plate, the plate will assume the position shown in FIGURE 1 in which a portion of the plate on one side of the bend line is drawn against the base of the container due to the magnetic attraction of'the magnet. As the bar rotates, it will pass beneath the portion of the plate on the other side of the bend line and this portion will be attracted to the bottom of the container. Referring to FIGURE 1, as the magnet 21 moves to the other side of the shaft 17, the portion of the plate which is shown raised from the bottom of the container will be drawn towards the container and the portion shown as being against the bottom of the container will rise. Thus, as the magnet 21 rotates beneath the container on opposite sides of a bend line in the plate 10, the plate will rock about the bend line. This rocking motion of the plate stirs the liquid in the container.

Preferably the motor 7 is a variable speed motor so that the rate of rotation of the bar 18 can be adjusted to vary the amount of stirring given to the liquid.

The use of a rotating channel bar magnet as a magnetic field generator has important advantages over field generators heretofore used in magnetic circuits. The channel bar magnet provides strong coupling between it and a stirring device in a container for liquid to be stirred and it can be used under containers having varying diameters.

While we have described a presently preferred embodiment of our invention, it is to be understood that it may be otherwise variously embodied within the scope of the appended claims.

We claim:

1. A stirrer for stirring liquid in a container made of non-magnetic material comprising,

(A) a base of non-magnetic material to support the container (B) a plate of magnetic material (1) positioned within the container, and

(2) being bent along a line extending across the plate,

(3) the portions of the plate extending from the bend line forming a dihedral angle between them of more than 90, and

(C) means for generating and moving a magnetic field beneath said base for alternately attracting portions of aid plate on opposite sides of said bend line towards said base to cause the plate to rock about said bend line.

2. A stirrer as described in claim 1 in which said plate is circular and in which the bend line is along a diameter of the plate.

3. A stirrer as described in claim 1 in which said plate is bent along a second bend line in a direction opposite to that in which the plate was bent along the first bend line, said second bend line extending. across the plate and at an angle to the first bend line, and in which portions of the plate extending from the tWo bend lines form an hyperbolic paraboloid.

4. A stirrer as described in claim 3 in which said two bend lines extend at right angles to each other,

5. A stirrer for stirring liquids in a container made of non-magnetic material comprising,

(A) a base of non-magnetic material to support the container (B) a plate of magnetic material (1) positioned within the. container, and

(2) being bent along a line extending across the plate,

(3) the portions of the plate extending from the bend line forming a dihedral angle between them of more than (C) a motor (1) positioned beneath the base, and

(2) having a vertically extending drive shaft,

(D) a bar (1) positioned between the base and the motor,

(2) mounted at the center of its mass on said motor shaft for rotation in a plane generally parallel to said base,

(3) a portion of said bar one one side of its center being magnetized (E) whereby upon rotation of the bar beneath said base the magnet will attract alternately portions-of the plate on opposite sides of the bend line of the plate and cause the plate to rock about said bend line.

6. A stirrer as described in claim 5 in which the magnetized portion of the bar is a channel bar magnet.

'7. A magnetic field generator for creating and moving a magnetic field in a circular path comprising,

(A) a channel bar magnet,

(B) meansadjacent one end of said magnet for rotating said magnet in a circular path and about an axis extending at right angles to the plane of said path, and

(C) north and south poles on said magnet extending away from said axis of rotation and positioned parallel to but spaced from each other on said magnet.

8. A magnetic field generator as described in claim 7 and having a counterweight secured to said magnet and extending through and beyond said axis of rotation.

9. A stirring plate comprising a plate of magnetic material bent along two bend lines extending across the plate and at an angle to each other, said plate being bent along one bend line in a direction opposite to that in which it is bent along the other bendline whereby the portions of the plate extending from the two bend lines form a hyperbolic paraboloid.

10. A stirring plate as described in claim 9 in which said plate has a central opening.

References Cited by the Examiner UNITED STATES PATENTS 63 5,767 10/99 Gleason. 1,238,962 9/ 17 Twitchell. 1,989,019 1/35 OKeefie 25976 2,580,132 12/51 Seymour 25929 2,681,678 6/54 Hage l5138 X 3,088,716 5/63 Stott 259-144 CHARLES A. WILLMUTH, Primary Examiner. 

1. A STIRRER FOR STIRRING LIQUID IN A CONTAINER MADE OF NON-MAGNETIC MATERIAL COMPRISING, (A) A BASE OF NON-MAGNETIC MATERIAL TO SUPPORT THE CONTAINER 